Evolution of helimagnetic correlations when approaching the quantum critical point of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>Mn</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi>Fe</mml:mi></mml:mrow><mml:mi>x</mml:mi></mml:msub><mml:mi>Si</mml:mi></mml:math>

We present a comprehensive investigation of the evolution helimagnetic correlations in Mn$_{1-x}$Fe$_x$Si with increasing doping. By combining polarised neutron scattering and high resolution Neutron Spin Echo spectroscopy we investigate three samples $x$=0.09, 0.11 0.14, i.e. compositions on both sides concentration $x^* \sim 0.11$ where Bragg peaks disappear between $x^*$ quantum critical $x_C 0.17$, $T_C$ vanishes. find that abrupt disappearance long range helical periodicity at $x^*$, does not affect precursor fluctuating correlations. These build up decreasing temperature similar way as for parent compound MnSi. Also dynamics bears strong similarities to The analysis our results indicates frustration, possibly due achiral RKKY interactions, increases Fe argue this effect explains expansion phase $x$ $x^*$.